What scale should I use for a small diorama, and how does this affect lighting etc
I would recommend using a scale such as real-life dioramas use. I'd say a scale of 0.25 or 2.5 blender cm for a real-world meter. Just a guestimate. It mostly depends on what you want in the art piece.
Your main limitation with doing life-size landscapes is &quot;clipping.&quot; Basically, the render system cannot keep calculating the view out into space forever, so past a certain distance it decides to start ignoring whatever's farther on. Get a look at this by making a giant cube or an ANT Landscape, then watching parts of it disappear as you get farther away from them.
If you want to do life-size, you can turn up the clipping limit on the camera to an extent, but for a better solution you can use &quot;mist&quot; to make the clipping effect not so prominent. This is like what Minecraft does where farther away things gradually become more transparent to the sky background (except with Minecraft it's not so much OpenGL as the system memory for how much world is loaded).